The present invention relates to side bearings for use in a railway truck, and more particularly to a multi-rate side bearing for use in a railway truck.
Typical side bearings in railway trucks comprise two rigid supports mounted on the upper side of the truck bolster on either side of the center plate. These supports may contact a roller or other low friction device or material. A corresponding member extends downward from the car bolster. Under normal car operation, the side bearing members are out of contact with the car bolster, the car load being carried by the center plate. However, under certain operating conditions leading to tilted car operation or car rocking, the side bearings come into contact to prevent extreme tilting which may lead to the car tipping over. Normally, however, the car is balanced in equilibrium on the center plate, and is free to rock about the longitudinal axis of the car.
Auxiliary side bearings located on the truck bolster between the center plate and the typical side bearings have been proposed for further car stabilization. Such auxiliary side bearings are shown in U.S. Pat. Nos. 3,400,669; 3,406,641 and 3,533,359. The object of such auxiliary side bearings is to provide improved resistance to rocking and accordingly improved load sharing laterally cross the truck bolster.
Studies have indicated that enhanced lateral stability, curving and roll stability can be achieved by specific combinations of primary and secondary suspension stiffness and damping parameters. Further, the truck bolster-car body yaw stiffness and damping are also seen to have significant influence on curving and lateral stability.
The secondary suspension system of a railway car truck consists of the main springs supporting the bolster within the side frames. This secondary suspension system of the railway car truck can be designed to provide satisfactory control of roll stability, longitudinal pitch and vertical ride quality by appropriate selection of spring rates and friction damper forces. The specific values of these parameters are dependent on vehicle weight and design, as well as such outside conditions as track geometry.
The present day railway car truck is unable to provide the desired low lateral spring rate between the empty car body and itself, since the lateral and vertical stiffness and damping forces are provided by the same springs and friction elements, although at differing rates. The introduction of constant contact side bearings provided a means of controlling truck hunting, but this was accomplished at the expense of curving performance. This is believed by some to contribute to derailment in curving, especially at low speeds.
The present invention overcomes the problems of known side bearings and provides desired stability and damping.